# Radical Mechanisms of Iron-Sulfur Proteins

> **NIH NIH R35** · PENNSYLVANIA STATE UNIVERSITY, THE · 2021 · $298,215

## Abstract

PROJECT SUMMARY
Elaborations of unactivated carbon centers are among the most demanding reactions that enzymes catalyze.
These reactions generally involve radical intermediates, often produced by strategic abstraction of substrate
hydrogen atoms (H·). A prevalent strategy to cleave C–H bonds possessing homolytic bond-dissociation
energies (BDEs) in excess of 95 kcal/mol involves intermediates derived from the reaction of O2 with transition
metal cofactors. A distinct strategy, predominant in the anaerobic world and still important in aerobes,
employs a 5'-deoxyadenosyl 5'-radical as the H· abstractor. This radical is generated via the homolysis of
adenosylcobalamin (AdoCbl) or the reductive cleavage of S-adenosylmethionine (SAM). Those enzymes
employing SAM to catalyze radical-dependent reactions belong to the so-called radical SAM (RS) superfamily,
which contains almost 114,000 individual sequences that encompass at least 65 distinct reactions. Moreover,
the number of enzymes and reactions catalyzed by members of the superfamily are increasing at an amazing
pace as sequences of new genomes become available. The work described herein builds on and advances work
from our laboratory on the characterization of some of the most novel reactions within the superfamily,
including those involved in tRNA and ribosome modification, lipoic acid biosynthesis, the biosynthesis of
several antibiotics, and antibiotic resistance. Specific objectives will be to i) elucidate how methylation of
unactivated carbon and phosphorus atoms takes place, and provide rationale for the strategy employed for
each type of methyl acceptor; ii) formulate methods to determine substrates for the many unannotated radical
SAM methylases; iii) elucidate how iron-sulfur clusters are used as sources of sulfur atoms during sulfur
insertion reactions and to determine how they are resynthesized after each turnover; iv) elucidate the pathway
for the biosynthesis of the thiopeptide antibiotic, nosiheptide; and v) begin to characterize several radical SAM
enzymes from humans that play important roles in health and disease.

## Key facts

- **NIH application ID:** 10131209
- **Project number:** 5R35GM122595-05
- **Recipient organization:** PENNSYLVANIA STATE UNIVERSITY, THE
- **Principal Investigator:** SQUIRE J. BOOKER
- **Activity code:** R35 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $298,215
- **Award type:** 5
- **Project period:** 2017-04-01 → 2022-03-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10131209

## Citation

> US National Institutes of Health, RePORTER application 10131209, Radical Mechanisms of Iron-Sulfur Proteins (5R35GM122595-05). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/10131209. Licensed CC0.

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